He is a talented British citizen who has long worked on digital wealth research with famous colleagues like Satoshi Nakamoto, Hal Finney and David Chaum.
He didn't actually work "with" any of these 3; when the source you mentioned says "worked alongside" them, it means that they were all active in cryptographic research within the same decade.
He is a great man though, but i just unfollow him in twitter because he is a bit annoying. Every day he posts nearly 10 tweets including retweets. I don’t like the followings who post too many tweets (>4) per day.